A principal object of the present invention is a design elements sequence for tire treads producing limited noise and a related design method. The rolling surface of the tires for road vehicles, or tread, is endowed with a relief conformation, apt to confer to the tread the desired use characteristics, as a balance between road-grip, on dry surface and on wet surface or snowy surface, water elimination, resistance to wear and so on.
To obtain the aforementioned performances the surface of the tread presents in general, transverse grooves with respect to the circumference direction, delimiting full portions, that in the complex have a size, disposition and outline embodied usually in block forms and grooves disposed in one or more circumferential rows, with equal or different space between them, to cover the total width of the tread.
The presence of the blocks and of the grooves however is a source of noise during rolling, due to the periodic contact between the blocks and the road that can result in annoyance for the user. Such noise presents sonorous power characteristics and distribution in different frequencies which are typical of any tread design that generates it at a determined rotation speed.
It is known that with other characteristics being equal it is more acceptable to the listener to hear noise distributed over a large frequency field rather than a concentrated noise in a restricted frequency field.
Tread drawings have therefore been developed that present design elements composed with a groove extending in a transverse direction with respect to the circumference and endowed with a continuous full portion, in a circumferential sense, or more generally by a complex of groove and full portions that repeat with a design geometrically similar, which juxtaposition creates the entire circumference, endowed with different lengths and placed in particular order, in conformity with applicable principles of physics, which are able to generate an identified sonorous sound in extended frequencies in a vast field.
Examples of such tread drawings are disclosed in the U.S. Pat. Nos. 4,327,792 and 4,474,223.
The practice of tread design has shown that the best result is achieved, with the known tread drawings, with the use of a high number of different lengths of the design elements, disposed according to established rules, for example with 4 or 5 different lengths, or pitches.
The realization of many different pitches in a tread is however undesirable, introducing drawbacks of different origin, in particular making the manufacture of the relative molds more complex.